Average Weather in Boston Massachusetts, United States
In Boston, the summers are warm, the winters are chilly and wet, and it is partly cloudy year round. Over the course of the year, the temperature typically varies from 23°F to 82°F and is rarely below 9°F or above 91°F.
The warm season lasts for 3.4 months, from June 5 to September 16, with an average daily high temperature above 73°F. The hottest day of the year is July 21, with an average high of 82°F and low of 67°F.
The cold season lasts for 3.4 months, from December 3 to March 15, with an average daily high temperature below 45°F. The coldest day of the year is January 29, with an average low of 23°F and high of 36°F.
Average High and Low Temperature
The figure below shows you a compact characterization of the entire year of hourly average temperatures. The horizontal axis is the day of the year, the vertical axis is the hour of the day, and the color is the average temperature for that hour and day.
Average Hourly Temperature
In Boston, the average percentage of the sky covered by clouds experiences mild seasonal variation over the course of the year.
The clearer part of the year in Boston begins around June 25 and lasts for 4.4 months, ending around November 6. On September 6, the clearest day of the year, the sky is clear, mostly clear, or partly cloudy 64% of the time, and overcast or mostly cloudy 36% of the time.
The cloudier part of the year begins around November 6 and lasts for 7.6 months, ending around June 25. On May 24, the cloudiest day of the year, the sky is overcast or mostly cloudy 54% of the time, and clear, mostly clear, or partly cloudy 46% of the time.
Boston does not experience significant seasonal variation in the frequency of wet days (i.e., those with greater than 0.04 inches of liquid or liquid-equivalent precipitation). The frequency ranges from 23% to 33%, with an average value of 28%.
Among wet days, we distinguish between those that experience rain alone, snow alone, or a mixture of the two. Based on this categorization, the most common form of precipitation throughout the year is rain alone, with a peak probability of 33% on May 24.
Daily Chance of Precipitation
To show variation within the months and not just the monthly totals, we show the rainfall accumulated over a sliding 31-day period centered around each day of the year. Boston experiences some seasonal variation in monthly rainfall.
Rain falls throughout the year in Boston. The most rain falls during the 31 days centered around October 23, with an average total accumulation of 3.9 inches.
The least rain falls around January 24, with and average total accumulation of 2.2 inches.
Average Monthly Rainfall
We report snowfall in liquid-equivalent terms. The actual depth of new snowfall is typically between 5 and 10 times the liquid-equivalent amount, assuming the ground is frozen. Colder, drier snow tends to be on the higher end of that range and warmer, wetter snow on the lower end.
As with rainfall, we consider the snowfall accumulated over a sliding 31-day period centered around each day of the year. Boston experiences some seasonal variation in monthly liquid-equivalent snowfall.
The snowy period of the year lasts for 4.9 months, from November 13 to April 11, with a sliding 31-day liquid-equivalent snowfall of at least 0.1 inches. The most snow falls during the 31 days centered around January 26, with an average total liquid-equivalent accumulation of 0.9 inches.
The snowless period of the year lasts for 7.1 months, from April 11 to November 13. The least snow falls around August 4, with an average total liquid-equivalent accumulation of 0.0 inches.
Average Liquid-Equivalent Monthly Snowfall
The length of the day in Boston varies significantly over the course of the year. In 2017, the shortest day is December 21, with 9 hours, 5 minutes of daylight; the longest day is June 21, with 15 hours, 17 minutes of daylight.
Hours of Daylight and Twilight
The earliest sunrise is at 5:06 AM on June 14, and the latest sunrise is 2 hours, 15 minutes later at 7:21 AM on November 4. The earliest sunset is at 4:11 PM on December 9, and the latest sunset is 4 hours, 14 minutes later at 8:25 PM on June 26.
Daylight saving time (DST) is observed in Boston during 2017, starting in the spring on March 12, lasting 7.8 months, and ending in the fall on November 5.
Sunrise & Sunset with Twilight and Daylight Saving Time
We base the humidity comfort level on the dew point, as it determines whether perspiration will evaporate from the skin, thereby cooling the body. Lower dew points feel drier and higher dew points feel more humid. Unlike temperature, which typically varies significantly between night and day, dew point tends to change more slowly, so while the temperature may drop at night, a muggy day is typically followed by a muggy night.
Boston experiences significant seasonal variation in the perceived humidity.
The muggier period of the year lasts for 3.3 months, from June 12 to September 21, during which time the comfort level is muggy, oppressive, or miserable at least 10% of the time. The muggiest day of the year is August 2, with muggy conditions 39% of the time.
The least muggy day of the year is February 23, when muggy conditions are essentially unheard of.
Humidity Comfort Levels
This section discusses the wide-area hourly average wind vector (speed and direction) at 10 meters above the ground. The wind experienced at any given location is highly dependent on local topography and other factors, and instantaneous wind speed and direction vary more widely than hourly averages.
The average hourly wind speed in Boston experiences mild seasonal variation over the course of the year.
The windier part of the year lasts for 5.9 months, from October 24 to April 22, with average wind speeds of more than 3.7 miles per hour. The windiest day of the year is February 20, with an average hourly wind speed of 4.9 miles per hour.
The calmer time of year lasts for 6.1 months, from April 22 to October 24. The calmest day of the year is July 31, with an average hourly wind speed of 2.6 miles per hour.
Average Wind Speed
The predominant average hourly wind direction in Boston is from the west throughout the year.
Boston is located near a large body of water (e.g., ocean, sea, or large lake). This section reports on the wide-area average surface temperature of that water.
The average water temperature experiences significant seasonal variation over the course of the year.
The time of year with warmer water lasts for 3.1 months, from June 25 to September 27, with an average temperature above 60°F. The day of the year with the warmest water is August 8, with an average temperature of 66°F.
The time of year with cooler water lasts for 3.9 months, from December 27 to April 23, with an average temperature below 44°F. The day of the year with the coolest water is March 2, with an average temperature of 38°F.
Average Water Temperature
This section discusses the total daily incident shortwave solar energy reaching the surface of the ground over a wide area, taking full account of seasonal variations in the length of the day, the elevation of the Sun above the horizon, and absorption by clouds and other atmospheric constituents. Shortwave radiation includes visible light and ultraviolet radiation.
The average daily incident shortwave solar energy experiences extreme seasonal variation over the course of the year.
The brighter period of the year lasts for 3.5 months, from May 5 to August 21, with an average daily incident shortwave energy per square meter above 5.8 kWh. The brightest day of the year is June 30, with an average of 6.8 kWh.
The darker period of the year lasts for 3.3 months, from November 3 to February 12, with an average daily incident shortwave energy per square meter below 2.7 kWh. The darkest day of the year is December 24, with an average of 1.6 kWh.
Average Daily Incident Shortwave Solar Energy
For the purposes of this report, the geographical coordinates of Boston are 42.358 deg latitude, -71.060 deg longitude, and 10 ft elevation.
The topography within 2 miles of Boston contains only modest variations in elevation, with a maximum elevation change of 118 feet and an average elevation above sea level of 10 feet. Within 10 miles contains only modest variations in elevation (502 feet). Within 50 miles contains significant variations in elevation (2,037 feet).
The area within 2 miles of Boston is covered by artificial surfaces (77%) and water (23%), within 10 miles by artificial surfaces (65%) and water (29%), and within 50 miles by trees (39%) and water (33%).
This report illustrates the typical weather in Boston, based on a statistical analysis of historical hourly weather reports and model reconstructions from January 1, 1980 to December 31, 2016.
Temperature and Dew Point
There are 3 weather stations near enough to contribute to our estimation of the temperature and dew point in Boston.
For each station, the records are corrected for the elevation difference between that station and Boston according to the International Standard Atmosphere , and by the relative change present in the MERRA-2 satellite-era reanalysis between the two locations.
The estimated value at Boston is computed as the weighted average of the individual contributions from each station, with weights proportional to the inverse of the distance between Boston and a given station.
The stations contributing to this reconstruction are: Logan International Airport (88%, 4.1 kilometers, east); East Milton (6%, 17 kilometers, south); and Lawrence G Hanscom Field (7%, 23 kilometers, northwest).
All data relating to the Sun's position (e.g., sunrise and sunset) are computed using astronomical formulas from the book, Astronomical Tables of the Sun, Moon and Planets , by Jean Meeus.
All other weather data, including cloud cover, precipitation, wind speed and direction, and solar flux, come from NASA's MERRA-2 Modern-Era Retrospective Analysis . This reanalysis combines a variety of wide-area measurements in a state-of-the-art global meteorological model to reconstruct the hourly history of weather throughout the world on a 50-kilometer grid.
Land Use data comes from the Global Land Cover SHARE database , published by the Food and Agriculture Organization of the United Nations.
Elevation data comes from the Shuttle Radar Topography Mission (SRTM) , published by NASA's Jet Propulsion Laboratory.
Names, locations, and time zones of places and some airports come from the GeoNames Geographical Database .
Time zones for aiports and weather stations are provided by AskGeo.com .
Maps are © Esri, with data from National Geographic, Esri, DeLorme, NAVTEQ, UNEP-WCMC, USGS, NASA, ESA, METI, NRCAN, GEBCO, NOAA, and iPC.